The short answer is no. The long answer is yes, but there are two main factors to consider before placing a raised garden bed on a timber deck: weight and water.
- Weight: The raised garden bed cannot weight more than the bearing load of the deck. Timber decks built within the parameters of the Australian Standard can support the weight of 200Kg per square metre. Blended topsoil weighs approximately 1000Kg per cubic metre. The raised garden bed, therefore, has to be 20cm in height or less.
- Water: if the timber deck is in permanent contact with water, this will result in fast decay of the wood. The excess water needs to be drained off the timber or left to evaporation, or the garden bed has to have a wicking system.
To conclude: if the timber deck is built to support a load of 500Kg per square metre, it is possible to place a raised garden bed 450mm high with a wicking system. If unsure of the bearing load, the safest option is to use a planter with self-watering pots like this.